JPH0514970B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a tracking servo device, and particularly to a tracking servo device that records and/or plays back information signals using a light beam. The present invention also relates to a device for controlling the tracking of a light beam based on a guide track recorded in advance on an information signal recording disk (hereinafter referred to as a disk).

2. Description of the Related Art When recording an information signal on a disk using a light beam, it has been conventional to form a guide track with virtually no information on the disk in advance, and record the information signal while being guided by this guide track during recording. known (for example, JP-A-49-113601).

However, in the conventional tracking servo device described above, when recording information signals using the main light beam, the conditions for the leading sub-light beam and the following sub-light beam are different (only the trailing sub-light beam is the main light beam). (influenced by the pits recorded by the light beam), which caused the problem that a correct tracking error signal could not be obtained. In addition, an information signal recording pit is formed in the guide track, which is a groove with a depth of λ/8 (where λ is the wavelength of the light beam), and the ±1st-order diffracted light emitted when the light beam irradiates the guide track. A method of tracking and controlling a light beam using light intensity is also conventionally known. However, in this conventional method, when the light beam crosses the guide track during playback, etc., the first-order diffracted light may or may not come out between the groove portion where the guide track is formed and the non-groove portion where the guide track is not formed. In some cases, the reflected light projected onto the 4-split detector becomes asymmetrical, resulting in malfunction of the focus servo based on the known astigmatism method. In other words, in a device that detects focus error using the astigmatism method,
If the above light beam traverses the guiding track,
The fact that the light-receiving surface of the 4-split detector is asymmetrical means that even in a focused state, the sum of the outputs of the detectors on one diagonal line is greater than the sum of the outputs of the detectors on the other diagonal line, which is not desirable. Nakatsuta. Therefore, in a device that uses this conventional tracking control method, it is not appropriate to use the astigmatism method for focus error detection, and a knife edge is set at the point where the reflected beam at the focused point is the narrowest, dividing the reflected beam into two. The light is received by an optical detector,
From this, it is preferable to use the knife edge method to obtain a focus error signal. However, this knife edge method requires precision in the knife edge, the detector, the focal length of the lens, etc., and therefore has the problem that the optical system becomes complicated.

Therefore, in Japanese Patent Application No. 60-141695, the present applicant proposed a tracking servo device which solved the above problems by performing tracking based on signals reproduced from a guide track consisting of intermittent pits. proposed. According to this proposed tracking servo device, tracking control is performed based on the reproduction signal from the guide track, which is an intermittent row of pits, so that the guide track, which consists of continuous grooves, can be used as an information signal recording track. Compared to the conventional method in which two sub-light beams are provided on both sides of the main light beam, the two sub-light beams are used to generate a signal corresponding to the prepit period, and the tracking error signal is obtained based on the prepit reproduction signal of the main light beam. 2
Differences in the conditions of the two secondary light beams are not a problem;
More accurate tracking control is possible, and compared to other conventional methods in which an information signal recording track is formed on one guide track, even when the light beam crosses the guide track during playback, the grooves in the guide track remain unchanged. Since the depth of It has many features such as being able to perform tracking control without complicating the optical system.

Problems to be Solved by the Invention However, in the proposed tracking servo device, when a light beam scans across an information signal recording track for special reproduction or the like, the tracking error signal is not detected in the information signal recording/reproduction. Each time the optical beam crosses one guide track, it becomes a sinusoidal signal that is inverted, so if an odd number of guide tracks are crossed, the tracking error signal must be inverted to return to the original correct polarity. There was a problem in that a counter-rotation path was required, making the circuit configuration somewhat complicated.

Therefore, an object of the present invention is to provide a tracking servo device that solves the above problems by using a zero-cross detector.

Means for Solving the Problems The tracking servo device according to the present invention includes a differential amplifier that differentially amplifies the reproduction signals of two adjacent guide tracks on both sides of the optical beam for recording and reproducing information signals. , a zero-crossing detector that detects the zero-crossing of the output signal of the differential amplifier and generates a switching pulse, and the crosstalk reproduction signal of the two adjacent guide tracks is converted into a half period of the switching pulse by the switching pulse. The polarity inverting means alternately inverts the polarity and outputs the output.

Operation: The output signal of the polarity reversing means is a tracking error signal at a predetermined level when the information signal recording/reproducing light beam is located between adjacent guide tracks. Here, when the light beam scans across the guide track, the output signal of the zero-crossing detector becomes a pulse that is inverted each time the light beam crosses the guide track, while the reproduction by the light beam The signal (RF signal) is a triangular wave-like reproduced signal whose slope is reversed each time it moves from one guide track to the next guide track. Therefore, the level of the tracking error signal from the polarity reversing means changes greatly each time the light beam crosses the guide track, and at other times the level changes gradually with the same slope. The signal waveform resembles a sawtooth wave. That is, since the tracking error signal at this time always has the same slope, there is no need for a circuit for inverting the tracking error signal each time the guide track is crossed.

Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a circuit diagram of an embodiment of a tracking servo device according to the present invention. In the same figure, the input terminal 10 is connected to the two-dot chain line shown in FIG. 2A on the disk.
The reproduction signal obtained by detecting the light intensity of the reflected light from the disk of the main light beam scanning between the adjacent guide tracks shown in 1 is further passed through a reduction filter. A guide track crosstalk reproduction signal is received. Further, input terminals 11 and 12 are provided with two tracking sub-light beams which are irradiated at positions opposite to each other by a certain distance in the track width direction, front and back in the scanning direction with respect to the main light beam. Reproduction signals of each of the two adjacent guide tracks as shown by a and b in FIG. Here, as shown in FIG _.
〜P ₁₅ , P ₂₁ 〜P ₂₅ , etc., pits P ₁₁ , P ₁₂ ,
..., P ₁₅ represent, for example, a group of pits in a part of the first guide track, and pits P ₂₁ , P ₂₂ , ... P ₂₅ represent two pits.
It shows a group of pits in a part of the main guide track,
These pits are recorded in advance (hereinafter, these pits will be referred to as prepits). The guide track is an intermittent row of these prepits, with two adjacent
Information signal recording tracks are formed between the guide tracks of the book by the main light beam during recording, and the information signal recording tracks are reproduced by the main light beam during reproduction. In FIG. 2A, -1 indicates the track center line of this information signal recording track position.

Here, to explain the guide track in more detail, in FIG. 6, which shows an enlarged part of the track pattern of the disk, two-dot chain lines 34 ₁ to 3
The shaded areas on both sides of the center line of each track of the information signal recording track indicated by 4 ₇ indicate prepits, and the starting and ending ends of each pre-pit coincide with the ending and starting ends of the radially adjacent prepits, respectively. There is. Therefore, the boundary line connecting the starting and ending ends of the prepits in the radial direction of the disk is shown in Figure 6.
As shown by the dashed dotted lines 35, they radiate at equal angular intervals in the radial direction around the center of the disc. Further, each prepit is a groove having a length corresponding to, for example, the recording wavelength of one horizontal scanning period, and the depth of the groove is selected to be 1/4 times the wavelength of the main and sub beams.

Returning to FIG. 1 again, input terminal 1
The reproduced signals a and b obtained by separately and simultaneously reproducing the two adjacent guide tracks entering 1 and 12 are the same as the pre-pit during the period when the two sub-light beams scan the pre-pit. A phase difference of λ/2 (where λ is the wavelength) occurs between the light reflected inside the groove and the light reflected outside the groove, so the light intensity of the reflected light is canceled out and greatly attenuated. On the other hand, during the period when the part without the prepits is scanned, the sub-light beam is reflected with almost no attenuation, so the light intensity of the reflected light is high.
Therefore, for example, it becomes a high level. In addition, Figure 2A
The relationship between the prepits P ₁₁ to _{P 25} in the center and the main light beam spot is for explanation only, and in reality, the deviation between each beam spot is extremely small.

The above reproduced signals a and b are square waves with a period corresponding to the prepit period as shown in Fig. 2B, but in reality, due to slight variations in the beam spot, etc. It will not be a waveform. However, even in this case, information on the ends of the prepits P ₁₁ to _{P 25} can be obtained from the edges of the reproduced signals a and b. Note that there is a relative phase shift in the reproduced signals a and b because the two sub-light beams are slightly shifted back and forth in the track direction, but this can be ignored for practical purposes.

The above reproduced signals a and b are supplied to a differential amplifier 15 through amplifiers 13 and 14, where they are differentially amplified and then supplied to a non-inverting input terminal of an operational amplifier 16 constituting a zero-cross detector. The operational amplifier 16 has its inverting input terminal grounded, and outputs a high level signal when the output signal of the differential amplifier 15 is higher than the ground level (zero cross level), and outputs a low level signal when the output signal is lower than the ground level (zero cross level). Therefore, from the operational amplifier 16, a zero-crossing detection pulse (not shown as c in FIG. 2B) having a waveform substantially similar to that of the reproduced signal a is taken out. That is, this pulse c is a square wave that goes high level corresponding to the prepits on one side of the guide tracks on both sides of the information signal recording track and goes low level corresponding to the prepits on the other side. It has a period corresponding to , and is applied to the switch circuit 18 as a switching pulse.

On the other hand, the crosstalk reproduction signal of the guide track caused by the main light beam entering the input terminal 10 is supplied to an AGC control circuit 21, which will be described later, and is also supplied to a common terminal of a switch circuit 18 through a DC cut amplifier 17. When the main light beam is correctly scanning the position between two adjacent guide tracks, a part of the main light beam spot hits the prepits, and the amount of reflected light decreases slightly, but the amount of light attenuation is As explained with the figure, since the end of the prepits is on the boundary line, the position remains constant even when transitioning from one of the two guide tracks to one of the other tracks. . In other words, even though prepits are recorded intermittently, the amount of reflected light of the principal light beam is not affected at all.

Now, for convenience of explanation, it is assumed that the spot caused by the main light beam sequentially traces the positions indicated by ``C'' to ``C'' in FIG. 2A, then the output signal waveform of the DC cut amplifier 17 becomes as shown by d in FIG. 2B. When the main light beam spot is located at the positions indicated by A to E in FIG. Prepit as shown in Figure 2B.
When the main light beam spot falls on P ₁₁ , P ₁₂ , and P ₁₃ (A, C, and H), the amount of reflected light is small, so the level is low, and at positions B and D, the pre-pit is
It is at a high level because it has never been in P ₂₁ or P ₂₂ . In addition, between the top and bottom, the main light beam spot is shifted toward the prepits of the lower second guide track, and the waveform of the output signal d changes depending on the presence or absence of the lower prepits P ₂₃ and P ₂₄ . changes as shown in FIG. 2B. Furthermore, nu indicates the position when the main light beam spot is at its optimum position, and since the main light beam spot is slightly overlapping the pre-pit _P25 , the reproduced signal d is at its optimum position, as shown in FIG. 2B. At this time, the level is intermediate between the high level and the low level.

The switch circuit 18 receives the switching pulse C.
During the high level period, the input signal d is selectively outputted to the non-inverting input terminal of the differential amplifier 19, and during the low level period, the input signal d is selectively outputted to the inverting input terminal of the differential amplifier 19. As a result, the differential amplifier 19
The signal d input to the non-inverting input terminal of is in phase,
On the other hand, the signal d input to the inverting input terminal is taken out in reverse phase, and the output signal of the differential amplifier 19 becomes as shown by the solid line e in FIG. 2B. That is, when the output signal e of the differential amplifier 19 shown in FIG. 2B is lower than the center level shown by the two-dot chain line, the main light beam spot shifts upward, and when the level is high, the main light beam spot shifts downward. This is a tracking error signal corresponding to a tracking deviation, which indicates that there is no tracking deviation when it is at the center level.

This tracking error signal e is sent to the AGC circuit 20.
The level is controlled based on the control signal from the AGC control circuit 21. The AGC circuit 20 and the AGC control circuit 21 are circuits for compensating for variations in the amount of reflected light. The effects of fluctuations in , etc. are removed. The output tracking error signal of the AGC circuit 20 is supplied to a tracking device 24 through an equalizer circuit 22 and an amplifier 23, where the main light beam and the two sub-light beams are kept in the same positional relationship. The optical paths of the three light beams are slightly displaced in the track width direction so that the main light beam scans the information recording track. In this way, the main light beam is tracked and controlled so that it always scans the position shown in FIG. 2A.

Note that the tracking control according to this embodiment is performed not only when an information signal recording track is formed between two adjacent guide tracks, but also when reproducing the recorded information signal. This process is also performed when recording new information signal recording tracks between guide tracks. Furthermore, during the above reproduction, the information signal from the information signal recording track is simultaneously reproduced by the main light beam along with the information recorded on the guide track, although the band of the latter reproduction information signal (RF signal) is on the order of MHz. On the other hand, the crosstalk reproduction information from the guide track is on the order of several kHz, and only the reproduction information from the guide track is frequency-selected by a band filter (not shown) and is supplied to the input terminal 10 shown in FIG.

Next, the operation when a light beam traverses a plurality of guide tracks for high-speed search etc. will be explained. An example will be explained in which the main light beam traverses four guide tracks in the order 1→2→3→4→5 as shown by the solid line in FIG.
Here, numbers 1 to 5 each indicate that the main light beam is located at a position on the track center line of the information signal recording track (a position where there is no track deviation). Also, the third
In the figure, a rectangular portion indicates a prepit. When the main light beam draws a scanning locus as shown by the solid line in FIG. 3, the crosstalk reproduction signal of the guide track by the main light beam extracted from the DC cut amplifier 17 shown in FIG. As shown by ', when the main light beam is on the track center line of the information signal recording tracks shown as 1 to 5 in FIG. It becomes a triangular wave with the minimum level when it is located on the preppit of the track. Incidentally, in FIG. 4, .about. indicates signals when the main beam is at positions 1 to 5 in FIG. 3.

On the other hand, since the two sub-light beams integrally draw the same scanning trajectory as the above-mentioned main light beam, each reproduction signal of the sub-beams input to the input terminals 11 and 12 in Fig. 1 is shown in Fig. 4. They form triangular waves with substantially opposite phases to each other, as shown by ′ and b′. Therefore, the signal waveform obtained by detecting the zero cross of the differentially amplified signal of the triangular waves a' and b' (which has the same waveform as a') using the operational amplifier 16 is as shown by c' in Fig. 4. , it becomes a rectangular wave that is inverted every time the main light beam is approximately located on the guide track. As a result, the output tracking error signal of the differential amplifier 19 becomes a sawtooth wave as shown by e' in FIG.

As can be seen from FIG. 4, this tracking error signal e' is at the center level when the main light beam is located on the track center line of the information signal recording track (indicated by ~), and when the main light beam is located on the guide track. It forms a sawtooth wave in which the level changes sharply every time the wave is located approximately at , and the slope is always in the same direction. Therefore, since the slope of the tracking error signal e' is always the same, there is no need for a circuit to invert the polarity of the tracking error signal even if the light beam crosses an odd number of guide tracks. Furthermore, the level of the tracking error signal e' changes rapidly each time the main light beam crosses the guide track, which indicates that the tracking capture range is extremely wide and the stability is good.

Note that the present invention is not limited to the above-mentioned embodiments, and includes various other modifications. For example, by configuring the optical detector as shown in FIG. 5, only one light beam spot can be detected. The present invention can also be applied to devices using. That is, in FIG. 5, the optical detector 2
6 is divided into four light receiving sections 26a to 26d, and an information signal recording track (or information signal recording track) is sent to an output terminal 28 from an adder 27 that adds and synthesizes each output signal of the light receiving sections 26a to 26d, respectively. A reproduced signal is obtained from the position on the disk that should become . Also, of the two guide tracks adjacent to this information signal recording track (or the position on the disk where the information signal recording track should be), the reflected light from one of the guide tracks is received by the light receiving sections 26a and 26d. , the reflected light from the other guide track is transmitted to the light receiving sections 26b and 2.
The light is received at 6c. Therefore, the crosstalk reproduction signal of one of the guide tracks is taken out to the output terminal 30 from the adder 29 which adds and synthesizes the output signals of both the light receiving sections 26a and 26d, and at the same time, both the output signals of the light receiving sections 26b and 26c are output. The crosstalk reproduction signal of the other guide track is taken out to an output terminal 32 from an adder 31 that adds and synthesizes the signals.

Effects of the Invention As described above, according to the present invention, when a light beam traverses multiple guide tracks during high-speed search, etc., the tracking error signal can be made into a sawtooth wave with the same slope at all times, thereby reducing the tracking error. A circuit for reversing the polarity of the signal can be eliminated, and the device can therefore be constructed at low cost.Also, since the level of the tracking error signal changes sharply each time the light beam crosses the guide track, tracking is improved. This device has features such as being able to extremely widen the capture range and stably performing the tracking control operation.

[Brief explanation of the drawing]

FIG. 1 is a block system diagram showing an embodiment of the apparatus of the present invention, FIGS. 2A and 2B are diagrams showing the positions of the light beam spots and signal waveforms of various parts of the block system shown in FIG. 1, and FIG. 3 4 shows an example of the light beam scanning trajectory when the light beam crosses multiple guide tracks, and FIG. 4 shows the block system shown in FIG. 1 when the light beam traces the scanning trajectory shown in FIG. 3. FIG. 5 is a diagram showing another example of an optical detector etc. that can be applied to the device of the present invention, and FIG. 6 is a diagram of the main parts of the disk proposed by the applicant that is applicable to the device of the present invention. FIG. 3 is a diagram showing an example track pattern. 10... Prepit crosstalk reproduction signal input terminal, 11, 12... Guide track reproduction signal input terminal, 15, 19... Differential amplifier, 16... Operational amplifier for zero cross detection, 18... Switch circuit, 26 ...Optical detector.

Claims (1)

[Claims] 1. A guide track, which is a row of pits, is formed in advance on both sides of the spiral or concentric track position where the information signal is to be recorded, and
During recording and reproduction of a recording disk in which recorded pits of adjacent guide tracks are alternately recorded in the radial direction, a light beam is used to scan the position of the track to be recorded and reproduced between the adjacent guide tracks. A tracking servo device that controls displacement in the track width direction based on a tracking error signal, and differentially amplifies the reproduction signals of the two adjacent guide tracks on both sides of the optical beam for recording and reproducing information signals. a differential amplifier, a zero-cross detector that detects a zero-cross of an output signal of the differential amplifier and generates a switching pulse having a period corresponding to the recorded pit period of the guide track, and a light beam for recording and reproducing the information signal. polarity inverting means for generating and outputting the tracking error signal by alternately inverting the polarity of the crosstalk reproduction signal of the two adjacent guide tracks by the switching pulse every half period of the switching pulse; A tracking servo device characterized by: